Problem: $ F = \left[\begin{array}{rrrr}2 & 4 & -1 & -2\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Answer: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 1 $\times$ 4 matrix.